1. Technical Field
The application relates to symbol timing methods, and more particularly, to symbol timing methods and apparatuses using the same, applied in multi-carrier receiving systems.
2. Related Art
A wireless communication system and a broadcast system are capable of transmitting information signals by a transmitter to a receiver via physical channels such as through air or by other interfaces. Due to non-ideal channel effect, such as multipath fading and reflection, the received signal usually has signal distortion. Orthogonal frequency division multiplexing schemes based on multi-carrier modulation may decrease multi-path fading and reflection. Recently, the application of a wire/wireless communication system and a broadcast system has become popularized. For example, Asymmetric Digital Subscriber Line (ADSL), Very-high-speed Digital Subscriber Line (VDSL), Digital Audio Broadcasting (DAB), Wireless Local Area Network (WLAN), 802.11a/g/n, Ultra Wideband (UWB), wireless communication system, Dedicated Short Range Communications (DSRC), Integrated Services Digital Broadcasting-Terrestrial (ISDB-T), Digital Video Broadcasting-Terrestrial/Handheld (DVB-T/H) and China Mobile Multimedia Broadcasting (CMMB) or other standards all adopt orthogonal frequency division multiplexing scheme.
FIG. 1 is a schematic diagram illustrating an orthogonal frequency division multiplexing symbol. In an orthogonal frequency division multiplexing symbol, a duplicated data is a copied section from the end of the symbol, and the duplicated data starts at the beginning of the symbol. The purpose of the duplicated data is to protect the orthogonal frequency division multiplexing symbol from inter-symbol interference (ISI) generated by multi-path fading and reflection in the channels. The duplicated data is also defined as a cyclic prefix (CP) or a guard interval (GI) and the length of guard interval is also defined as a GIL. For example, there are three choices for the number of carriers known as 2K-mode, 4K-mode and 8K-mode in a Digital Video Broadcasting Terrestrial/Handheld (DVB-T/H) and one of the 2K-mode, 4K-mode and 8K-mode respectively associates with four different kinds of the guard intervals. For example, the guard interval can be 1/32, 1/16, ⅛ or ¼ the length of a symbol. Normally, the length of the guard interval is larger than the longest length of the delay path in the multi-path fading and reflection of the channels.
The duplicated data may be used in the receiver to process the received signal such as a coarse symbol timing estimation and the carrier frequency offset estimation and so forth. A channel impulse response of the first channel may be selected for the coarse symbol timing procedure, but it is not the most powerful channel impulse response. Thus, a filter for a channel estimation module can include all the channel impulse responses of the channels for correct estimation of the coarse symbol timing procedure.
Note that the guard interval which is affected by the inter-symbol interference should be removed from the starting of the orthogonal frequency division multiplexing symbol before the receiver processes the signal. A correct coarse symbol timing position enables the Fast Fourier Transform (FFT) window timing correct. If the Fast Fourier Transform (FFT) window timing is not correct, the phase difference noise will be introduced. In slight degree the time will be prolonged to get the correct coarse symbol timing, but in serious degree the resolution of all the following data can not be correctly gotten.